Dendritic polymers have been used in the field of manufacturing protective coatings due to their unique structure which leads to the formation of high performance coatings. Protective coatings offer protection for a surface from damage by the elements such as water, snow, ice, heat, dirt, smog, organic waste, chemical attacks and acid precipitation.
As dendritic polymers are hyperbranched structures which can comprise a high number of reactive functional groups exposed at the peripheral edges of the dendritic polymer, they are considered as one of most promising resin systems for providing coating films having high cross-linking density and high surface protection performance.
Depending on the degree of branching, dendritic polymers may be classified into first, second, third, fourth or even fifth generation dendritic polymers. A first generation dendritic polymer may theoretically have a total of eight peripheral reactive functional groups, whereas a second generation polymer will have theoretically sixteen peripheral functional groups, and whereas a third generation polymer will theoretically have thirty two peripheral functional groups and so forth. The total number of peripheral functional groups per molecule is also referred to as the peripheral functionality.
Dendritic polymers can mimic the hydrodynamic volumes of spheres, and as such, they can be used to provide coatings of high molecular weights whilst maintaining relatively low viscosity. At the same time, dendritic polymers can be used to provide coatings with high cross-linking density while maintaining the flexibility of the coating.
Conventionally, protective coatings comprising dendritic polymers are provided as organic solvent-based coating systems due to the dendritic polymer's lack of solubility in water.
Such solvent-based systems provide excellent abrasion resistance, flexibility, adhesion, and chemical resistance. However, due to the presence of organic solvents which are volatile in nature, coatings prepared from solvent-based systems will typically emit an undesirably high level of volatile organic compounds (“VOC”). In recent years, ever stricter regulatory requirements in many countries have driven coating manufacturers to explore the possibilities of coating compositions that have low VOC emission levels. Thus, water-based coatings that do not involve the use of organic solvents have been contemplated in the art.
However, due to the hydrophobic nature of large polymers like dendritic polymers, at least some amount of ionic content is required to be grafted onto these polymers to allow the polymer compositions to be soluble in water.
One known method for incorporating ionic groups onto dendritic polymers is by reacting hydroxyl functional dendritic polymers with acid anhydrides followed by neutralization of the mixture. In this method, carboxyl groups are grafted onto the peripheral surface of the dendritic polymers to improve its solubility in water. In one known water-based dendritic polymer coating, the coating comprises a fluorine-containing dendritic polymer having at least one pendant fluorocarbon moiety and at least one pendant anionic moiety. Presumably, the presence of the anionic moieties improves the solubility of the dendritic polymer in water.
However, this additional modification step is cumbersome and results in added expenditure related to the procurement of required chemicals and solvents, for performing the modification step. Furthermore, some of the required chemicals and solvents are organic pollutants and their disposal would pose a problem logistically and environmentally.
More importantly, it has been observed that the incorporation of excess ionic groups, for example carboxyl groups, will adversely affect coating performance, especially with respect to the chemical resistance and water resistance of the coating.
Accordingly, there is a need to provide a polymer composition that overcomes, or at least ameliorates, one or more of the disadvantages described above.
In particular, it is an object of the present invention to provide an aqueous dispersible polymer composition that does not require an additional modification step for achieving solubility in an aqueous solvent, and at the same time, being capable of providing coatings that exhibit comparable, if not superior, performance when compared with conventional water-based coatings.